The England team doctor is alleged to have suggested screening squad members for thyroid and asthma-related conditions, only to be blocked by Premier League clubs.
Sportsmail has been told Dr Rob Chakraverty met the medical departments at several top clubs shortly after joining the Football Association in 2016 and proposed screening England players, raising suspicions he may have been seeking a medical requirement to legally offer performance-enhancing drugs.
All the clubs who met with Dr Chakraverty are understood to have raised objections and the idea was quietly shelved.
Some club doctors said that such screening was unnecessary as they already conducted extensive blood testing, while others were reluctant to give the FA more control over their players and cited a FIFA directive which gives clubs pre-eminence over national associations in medical matters.
At least one club medic raised ethical concerns amid suspicion that the screening could lead to attempts to give England players legal medication with performance-enhancing benefits.
Medication for hypothyroidism such as L-thyroxine and Cynomel has been shown to aid weight loss and recovery between sessions, enabling athletes to train harder, while asthma treatments such as salbutamol are known to improve aerobic performance.
FA sources confirmed on Friday night the England medical team are in a position to offer screening tests but only in collaboration with a player and his club, and that treatment is only provided when medically appropriate.
But a long-standing club medic told Sportsmail that screening specifically for hypothyroidism was unnecessary as the condition is so rare among men, being limited to one per cent of the population, and had aroused suspicions.
'They were trying to prove certain players had an underactive thyroid so they could give them medication that would enhance recovery,' the medic said. 'The clubs were scared by the moral issues so put a stop to it.
'In all my years in football I've never known of a player with an underactive thyroid. There was a backlash from the clubs and it didn't happen.'
Another experienced doctor at a different Premier League club shared similar concerns, although there was no suggestion of malpractice by anyone at the FA.
'The clubs didn't want the FA messing with their players and also thought it would set a dangerous precedent,' said the medic. 'The clubs conduct blood tests which could reveal signs of a thyroid issue, that may require further exploration. We didn't think it was necessary.'
Dr Chakraverty has worked as the senior doctor with the England team since joining the FA when Sam Allardyce was manager in 2016. He previously spent seven years at UK Athletics, where he worked closely with leading British athletes at the 2012 and 2016 Olympics.
Sportsmail revealed on Friday that several athletes have raised concerns about the governing body's willingness to suggest thyroid medication in particular, fearing it could be used as a way of obtaining a legal marginal gain. There is no suggestion that UK Athletics doctors have prescribed the medication unnecessarily.
The athletes who spoke to Sportsmail said suggestions about thyroid treatments were made by Chakraverty, who was UKA's chief medical officer between January 2013 and September 2016, and his successor Dr Noel Pollock.
Chakraverty admitted in 2017 that he had failed to properly record an injection of L-carnitine — a legal supplement — given to Mo Farah to 'help performance' before the 2014 London Marathon.